A new study shows that NK cells may be able to form adaptive memory and demonstrate specific antigen memory.
Innate immunity has long been considered the nonspecific first line of defense against an invading microorganism, while adaptive (or acquired) immunity is an antigen-specific immune response characterized by a memory that allows protection against a repeat exposure. Examples of cells of the innate immune response include natural killer (NK) cells, macrophages, neutrophils, and mast cells. T and B lymphocytes are cells of the adaptive immune system.
Previous results of research in laboratory mice and nonhuman primates have suggested that NK cells are capable of participating in adaptive immunity and demonstrate specific antigen memory. This implies that T and B lymphocytes may not be the only cells involved in adaptive immunity. Research was then conducted in mice with humanized immune cells and humans with a history of chickenpox (varicella zoster) infection.
The humanized mice were vaccinated with HIV-encoded envelope protein, and a control group was not vaccinated. The NK cells were collected 14 days later from the livers and spleens of the mice, cultured, and exposed to HIV envelope protein, influenza virus, ovalbumin, or nothing. The researchers found that the NK cells from mice previously vaccinated with HIV envelope protein reacted when exposed again to the protein, but not when exposed to the other antigens. There was little or no reaction of exposed NK cells from mice that were not previously vaccinated.
The study conducted in humans was also intriguing. Individuals from the 40–60-year-old age group who had chickenpox during childhood were given an intradermal injection of varicella zoster virus glycoprotein antigen. Fluid from the formed blisters was collected from the study participants and NK cells isolated. A delayed-type hypersensitivity response was induced, and a large number of NK cells were found to have been recruited to the intradermal injection sites decades after the individuals had chickenpox. Understanding the role of NK cells in adaptive immunity will provide another target for the development of more robust vaccines involving the actions of T, B, and NK cells and may help overcome the challenges to develop more effective vaccines.
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Reference: Innate Immune Cells May Actually Remember Their Targets. (2019). The Scientist Magazine®. Retrieved 25 June 2019, from https://www.the-scientist.com/news-opinion/innate-immune-cells-may-actually-remember-their-targets-65859